Misplaced Pages

#907092

32-464: Like most lectins, ConA is a homotetramer : each sub-unit (26.5 kDa , 235 amino-acids , heavily glycated) binds a metallic atom (usually Mn and a Ca). It has the D 2 symmetry. Its tertiary structure has been elucidated, as have the molecular basis of its interactions with metals as well as its affinity for the sugars mannose and glucose are well known. ConA binds specifically α-D-mannosyl and α-D-glucosyl residues (two hexoses differing only in

64-410: A concurrent loss of activity or stability. Such noncovalent ConA-glycoenzyme couplings may be relatively easily reversed by competition with sugars or at acidic pH. If necessary for certain applications, these couplings can be converted to covalent bindings by chemical manipulation. A report from Taiwan (2009) demonstrated potent therapeutic effect of ConA against experimental hepatoma (liver cancer); in

96-429: A fluorescently labeled streptavidin . (Streptavidin binds to four biotins per molecule.) This tetramer reagent will specifically label T cells that express T cell receptors that are specific for a given peptide-MHC complex. For example, a Kb/FAPGNYPAL tetramer will specifically bind to Sendai virus specific cytotoxic T cell in a C57BL/6 mouse. Antigen specific responses can be measured as CD8+, tetramer+ T cells as

128-430: A fraction of all CD8+ lymphocytes. The reason for using a tetramer, as opposed to a single labeled MHC class I molecule is that the tetrahedral tetramers can bind to three TCRs at once, allowing specific binding in spite of the low (1 micromolar) affinity of the typical class I-peptide-TCR interaction. MHC class II tetramers can also be made, although these are more difficult to work with practically. A homotetramer

160-532: A single active site. To convert conA to the mature form, jack bean asparaginyl endopeptidase cleaves the precursor of conA in the middle and ligates the two original termini. Concanavalin A interacts with diverse receptors containing mannose carbohydrates, notably rhodopsin, blood group markers , insulin receptors, the immunoglobulins and the carcino-embryonary antigen (CEA). It also interacts with lipoproteins . ConA strongly agglutinates erythrocytes irrespective of blood-group, and various cancerous cells. It

192-529: A tetramer is primarily determined by non covalent interaction. Hydrophobic effects , hydrogen bonds and electrostatic interactions are the primary sources for this binding process between subunits. For homotetrameric proteins such as sorbitol dehydrogenase (SDH), the structure is believed to have evolved going from a monomeric to a dimeric and finally a tetrameric structure in evolution. The binding process in SDH and many other tetrameric enzymes can be described by

224-433: Is a lymphocyte mitogen . Similar to phytohemagglutinin (PHA), it is a selective T cell mitogen relative to its effects on B cells. PHA and ConA bind and cross-link components of the T cell receptor , and their ability to activate T cells is dependent on expression of the T cell receptor. ConA interacts with the surface mannose residues of many microbes, including the bacteria E. coli , and Bacillus subtilis and

256-433: Is a protein with a quaternary structure of four subunits (tetrameric). Homotetramers have four identical subunits (such as glutathione S-transferase ), and heterotetramers are complexes of different subunits. A tetramer can be assembled as dimer of dimers with two homodimer subunits (such as sorbitol dehydrogenase ), or two heterodimer subunits (such as hemoglobin ). The interactions between subunits forming

288-443: Is a disease that develops as a complication of rhegmatogenous retinal detachment . PVR occurs in about 8–10% of patients undergoing primary retinal detachment surgery and prevents the successful surgical repair of rhegmatogenous retinal detachment. PVR can be treated with surgery to reattach the detached retina but the visual outcome of the surgery is very poor. A number of studies have explored various possible adjunctive agents for

320-552: Is a homotetrameric enzyme that can undergo intragenic complementation. An ASL disorder in humans can arise from mutations in the ASL gene, particularly mutations that affect the active site of the tetrameric enzyme. ASL disorder is associated with considerable clinical and genetic heterogeneity which is considered to reflect the extensive intragenic complementation occurring among different individual patients. Proliferative vitreoretinopathy Proliferative vitreoretinopathy ( PVR )

352-463: Is a protein complex made up of four identical subunits which are associated but not covalently bound. Conversely, a heterotetramer is a 4-subunit complex where one or more subunits differ. Examples of homotetramers include: Examples of heterotetramers include haemoglobin ( pictured ), the NMDA receptor , some aquaporins , some AMPA receptors , as well as some enzymes . Ion-exchange chromatography

SECTION 10

#1732875618908

384-415: Is formed from polypeptides produced by two different mutant alleles of a particular gene, the mixed multimer may exhibit greater functional activity than the unmixed multimers formed by each of the mutants alone. When a mixed multimer displays increased functionality relative to the unmixed multimers, the phenomenon is referred to as intragenic complementation . In humans, argininosuccinate lyase (ASL)

416-473: Is rich in RPE cells. The subretinal membranes are of two types. One forms as diffuse sheets, which are not contractile and either lack or contain very little ECM. The presence of this type of membrane does not usually affect retinal reattachment surgery. The retina can be reattached even with the membrane in place. The other type forms as very thick contractile membranes which pull at the retina. These are opaque and block

448-401: Is useful for isolating specific heterotetrameric protein assemblies, allowing purification of specific complexes according to both the number and the position of charged peptide tags. Nickel affinity chromatography may also be employed for heterotetramer purification. Multiple copies of a polypeptide encoded by a gene often can form an aggregate referred to as a multimer. When a multimer

480-462: The ability to migrate out into the vitreous. During this process the RPE cell layer-neural retinal adhesion and RPE-ECM ( extracellular matrix ) adhesions are lost. The RPE cells lay down fibrotic membranes while they migrate and these membranes contract and pull at the retina. All these finally lead to secondary retinal detachment after primary retinal detachment surgery. A number of studies have also shown that arachidonic acid metabolic cascade (one of

512-526: The alcohol on carbon 2) in terminal position of ramified structures from B-Glycans (rich in α-mannose, or hybrid and bi-antennary glycan complexes). It has 4 binding sites, corresponding to the 4 sub-units. The molecular weight is 104–112 kDa and the isoelectric point (pI) is in the range of 4.5–5.5. ConA can also initiate cell division (mitogenesis), primarily acting on T-lymphocytes, by stimulating their energy metabolism within seconds of exposure. ConA and its variants (found in closely related plants) are

544-498: The detached retina. The ECM laid on the vitreous side of the retina are referred to as epiretinal or preretinal membranes (ERM) and those laid down between the RPE layer and the photoreceptors are referred to as subretinal or retroretinal membranes (SRM) . The two membranes differ in composition in that the ERM is composed of RPE cells, glial cells, macrophages and fibrocytes , while the SRM

576-568: The expression of cyclooxygenases in both models of PVR, but also neutralized the changes of the retina and the choroid thickness caused by the injection of pro-inflammatory agents. PVR is graded as Grade A, B, or C by the Silicone Oil Study and as Grade A, B, C, or D by the Retina Society Terminology Committee . The RPE cells migrate out into the vitreous, proliferate excessively and lay down ECM on both side sides of

608-588: The gain in free energy which can be determined from the rate of association and dissociation. The above image shows the assembly of the four subunits (A,B,C and D) in SDH. Hydrogen bonding networks between subunits has been shown to be important for the stability of the tetrameric quaternary protein structure . For example, a study of SDH which used diverse methods such as protein sequence alignments , structural comparisons, energy calculations, gel filtration experiments and enzyme kinetics experiments, could reveal an important hydrogen bonding network which stabilizes

640-489: The light falling on the retina so the retinal reattachment surgery needs to be performed after manually peeling the membrane off. A number of cytokines such as tumor necrosis factor alpha (TNFα), transforming growth factor beta 2 (TGFβ 2 ), platelet derived growth factor (PDGF) and interleukins have been shown to play a role in PVR progression. TGFβ 2 levels have been shown to be elevated up to three times normal during

672-430: The major inflammatory cascades) is important in the development of PVR. COX-2 expression was found in human idiopathic epiretinal membranes. Phospholipase A2 and cyclooxygenase blocking reduced structural abnormalities of the rat retina in concanavalin model of PVR and reduced the frequency of membrane formation by 43% in the dispase model of PVR and by 31% in the concanavalin one. Lornoxicam not only normalized

SECTION 20

#1732875618908

704-558: The only proteins known to undergo a post-translational sequence arrangement known as Circular permutation in proteins whereby the N-terminal half of the conA precursor is swapped to become the C-terminal half in the mature form; all other known circular permutations occur at the genetic level. ConA circular permutation is carried out by jack bean asparaginyl endopeptidase, a versatile enzyme capable of cleaving and ligating peptide substrates at

736-409: The patient's risk for acquiring PVR is: 1 is added if the risk factor is present and 0 if the risk factor is absent. A patient is at a high risk for developing PVR if their PVR score is >6.33. During rhegmatogenous retinal detachment, fluid from the vitreous humor enters a retinal hole. The mechanisms by which retinal holes or tears form are not fully understood yet. The accumulation of fluid in

768-522: The prevention and treatment of PVR, such as methotrexate , although none have yet been licensed for clinical use. PVR was originally referred to as massive vitreous retraction and then as massive periretinal proliferation . The name proliferative vitreo retinopathy was provided in 1989 by the Silicone Oil Study group . The name is derived from proliferation (by the retinal pigment epithelial and glial cells ) and vitreo retinopathy to include

800-448: The progression of PVR. TGFβ 2 is the most predominant isoform in the eye and is secreted as a latent inactive peptide into the vitreous by epithelial cells of the ciliary body and the lens epithelium and is also produced by the RPE cells and the Muller cells of the retina. TGFβ 2 is known to induce EMT in RPE cells and fibrosis in the eye. Expression of PDGF in particular PDGF-AA

832-403: The protist Dictyostelium discoideum . It has also been shown as a stimulator of several matrix metalloproteinases (MMPs). ConA has proven useful in applications requiring solid-phase immobilization of glycoenzymes, especially those that have proved difficult to immobilize by traditional covalent coupling. Using ConA-couple matrices, such enzymes may be immobilized in high quantities without

864-408: The study by Lei and Chang, ConA was found to be sequestered more by hepatic tumor cells, in preference to surrounding normal hepatocytes. Internalization of ConA occurs preferentially to the mitochondria after binding to cell membrane glycoproteins, which triggers an autophagic cell death. ConA was found to partially inhibit tumor nodule growth independent of its lymphocyte activation; the eradication of

896-461: The subretinal space and the tractional force of the vitreous on the retina result in rhegmatogenous retinal detachment. During this process the retinal cell layers come in contact with vitreous cytokines. These cytokines trigger the ability of the retinal pigmented epithelium (RPE) to proliferate and migrate. The process involved resembles fibrotic wound healing by the RPE cells. The RPE cells undergo epithelial-mesenchymal transition (EMT) and develop

928-419: The tetrameric quaternary structure in mammalian SDH. In immunology , MHC tetramers can be used in tetramer assays , to quantify numbers of antigen-specific T cells (especially CD8+ T cells ). MHC tetramers are based on recombinant class I molecules that, through the action of bacterial BirA, have been biotinylated . These molecules are folded with the peptide of interest and β2M and tetramerized by

960-404: The tissues which are affected, namely the vitreous humor (or simply vitreous) and the retina . Predisposing factors for Postoperative PVR are preoperative PVR, aphakia , high levels of vitreous proteins, duration of retinal detachment before corrective surgery, the size of the retinal hole or tear, intra-ocular inflammation, vitreous hemorrhage, and trauma to the eye. An equation to calculate

992-410: The tumor in the murine in-situ hepatoma model in this study was additionally attributed to the mitogenic/lymphoproliferative action of ConA that may have activated a CD8+ T-cell-mediated, as well as NK- and NK-T cell-mediated, immune response in the liver. ConA intravitreal injection can be used in the modeling of proliferative vitreoretinopathy in rats. Homotetramer A tetrameric protein

Concanavalin A - Misplaced Pages Continue

1024-531: Was demonstrated that transformed cells and trypsin -treated normal cells do not agglutinate at 4 °C, thereby suggesting that there is a temperature-sensitive step involved in ConA-mediated agglutination. ConA-mediated agglutination of other cell types has been reported, including muscle cells , B- lymphocytes (through surface immunoglobulins ), fibroblasts , rat thymocytes , human fetal (but not adult) intestinal epithelial cells , and adipocytes . ConA

#907092